Abstract: Large Eddy Simulation（LES） method describing behaviour of the fluctuation of free surface in continuous casting mould was constructed.The accuracy of mathematical models was also verified by water experiments.The transient flow field and free surface fluctuations inside the mould were studied.Fluctuation height,velocity and turbulent energy of free surface were also quantitatively analyzed.The results show that the flow fields with unsteady characteristics affect transient fluctuation of free surface inside the mould.The free surface fluctuates sharply in the vicinity of the middle position between SEN nozzle and the narrow wall,and fluctuation height and velocity of free surface on both sides of SEN inside the mould show an asymmetrical distribution in the space-time range.